DESCRIPTION (Applicant's abstract): Proper folding of proteins (either newly synthesized or damaged in response to a stressful event) occurs in a highly regulated fashion. The major chaperones in this process, the 70- and 90-kDa heat shock proteins, are assisted by co-factors that modulate the folding machinery in a positive or negative manner. Dr. Patterson has recently identified a novel, developmentally regulated protein called CHIP (carboxyl terminus of Hsc70-interacting protein) that interacts with the molecular chaperones (Hsc70, Hsp70, and Hsp90) and negatively regulates their functions. CHIP interacts with the chaperones Hsc70, Hsp70, and Hsp90, and, in general, attenuates the most well characterized functions of these proteins. In addition, CHIP has novel effects on ubiquitination of Hsp substrates via an E3 ubiquitin ligase activity. Although it has been suggested that the chaperone and ubiquitin-proteasome pathways function cooperatively, the factors mediating this association have not been characterized. The principal investigator hypothesizes that CHIP links the chaperone and proteasome systems to regulate the balance between protein folding and degradation within the cell. To test the hypotheses, Dr. Patterson will characterize the effects of CHIP on Hsc70 function, and explore the novel observation that CHIP elicits atypical ubiquitylation of Hsc70 in vivo (Aim I). He will characterize the E3 ligase activity of CHIP biochemically and will identify the partner proteins that participate in this process (Aim II), and we will determine the cellular role for this novel E3 ligase activity (Aim III). To define the physiologic role of CHIP, Dr. Patterson has created mice deficient in CHIP by homologous recombination; he will observe the developmental and morphologic effects of CHIP in these mice and will test the physiologic responses of these mice to stress (Aim IV). These studies may provide insights into the pathogenesis of diseases, such as cancer, cystic fibrosis, and cardiovascular diseases, in which protein folding and degradation play a role.